1. Field of the Invention
The present invention relates to a virtual grid imaging method for eliminating scattered radiation effect and an imaging system thereof, and more particularly to a virtual grid imaging method and imaging system thereof capable of eliminating scattered radiation effect generated by high energy rays such as X-rays and gamma rays after passing through a to-be-detected object, which belongs to the field of digital image processing technology.
2. Description of Related Art
High energy rays including X-rays and gamma rays have a strong penetration power, capable of penetrating through many substances opaque to visible lights, such as inking sheet and timber. With this penetration power, the high energy rays are used to perform medical diagnosis and treatment, used to test nondestructive materials in industry, and widely used to analyze crystal structure and perform chemical analysis and researches on atomic structure through spectrum and absorption situation of the rays in the fundamental science and applied sciences.
When irradiating the to-be-detected object with high energy rays, after the rays penetrate through the to-be-detected object, not only primary radiation is generated, but scattered radiation is also generated. The scattered radiation generates extra exposure, which overlaps on the image of the rays as a “scattering fog”, thereby reducing the contrast and definition of the image of the rays, and reducing the noise-to-signal ratio at details of the image. The specific reducing degree depends on the intensity of the scattered radiation.
In order to alleviate adverse effects caused by the scattered radiation, several technical solutions have been researched. Taking the most commonly-used X-rays for an example, a special anti-scatter grid has been generally used at home and abroad. This type of anti-scatter grid is referred to as a grid, which is published by U.S. Pat. No. 1,164,987 the earliest. The grid is disposed between the to-be-detected object and an X-ray detector, allows the primary radiation from a focal point of the X-ray tube to pass through, but substantially absorbs scattered radiation from the to-be-detected object and incident in different angles. The grid is generally made of lead with a small volume and a high absorptivity. A medium between the absorbers is paper, fiber, aluminum, or a kind of inelastic foam with a high resistance. The latest technical development for the grid can be obtained with reference to documents such as Chinese Patent Application, entitled “Anti-scatter Grids for X-ray Equipments” (Application Number: 02126906.8, Date of Publication: Apr. 2, 2003).
With the anti-scatter gird, the scattered radiation generated in the to-be-detected object is reduced and the imaging quality is improved, however, the anti-scatter gird itself also blocks a portion of the X-rays that should be incident to the X-ray detector. In order to alleviate the adverse effects, the radiation dosage of the X-rays must be increased, which causes disadvantages in two aspects. In one aspect, the to-be-detected object, particularly patients and medical workers, suffers from an increased radiation, and in the other aspect, the requirements for the X-ray tube and high-voltage generator are increased, thereby the manufacturing cost of the X-ray detecting apparatus is increased.
In Chinese Patent Application, entitled “Anti-scatter X-ray Shielding used in CT Scanner” (Application Number: 02829542.0, Date of Publication: Sep. 21, 2005), an anti-scatter (AS) material used for absorbing X-rays between X-ray detector rows, and an AS material used for absorbing X-rays between X-ray detector columns are provided, in which the AS materials are respectively located between every two rows/columns of detectors. Furthermore, the thickness and/or height of the foil between rows can be different from the thickness and/or height of the foil between columns. Moreover, in Chinese Patent Application, entitled “Incoherent Scattering Eliminating Device Used in X-ray Phase Imaging Based on Energy Recognition” (Application Number: 200610024489.1, Date of Publication: Aug. 23, 2006), an incoherent scattering eliminating device used in X-ray phase imaging based on energy recognition is provided, which includes three parts: an X-ray generation and modulation system, a to-be-detected object fixing device, and a back-end X-ray modulation and detection system. This invention selects different filtering materials, and ensures that substantially no loss occurs in the valid X-rays, and almost all the primary radiation with a constant wavelength reach the X-ray detector, thereby eliminating the influences to the imaging quality caused by the incoherent scattering.